A semiconductor device includes a semiconductor substrate of a first conductivity type. A first semiconductor layer of a second conductivity type is on the semiconductor substrate. A buried semiconductor layer of the second conductivity type is on the first semiconductor layer. A second semiconductor layer of the second conductivity type is on the buried semiconductor layer. A trench extends through each of the second semiconductor layer, the buried semiconductor layer, and the first semiconductor layer, and into the semiconductor substrate. An insulating structure lines walls of the trench. A conductive filling in the trench is electrically coupled to the semiconductor substrate at a bottom of the trench.